1. Field of the Invention
The present invention relates to a method of manufacturing an optical memory device such as an optical card or an optical disc used as a large capacity data recording medium, and to an apparatus for the same.
2. Description of the Prior Art
An optical memory device comprises a substrate, a recording layer formed on this substrate, and a protective layer formed on this recording layer for protecting the same (see U.S. Pat. No. 4,544,835 and U.S. Pat. No. 4,680,460).
A method heretofore known of forming guide tracks used for writing and reading information to and from a sheet-like substrate to manufacture an optical memory device such as an optical card or an optical disc includes a process for continuously printing light and shade patterns for tracking on a sheet roll-like substrate material. In addition, a method heretofore known of forming groove-shaped guide tracks used for tracking utilizing diffraction of light includes a process for transcribing the shape of grooves onto a cut sheet-like or rolled sheet-like substrate material by means such as a 2P process (photopolymer process), a process for stamping the shape of grooves by directly pressurizing a substrate using a heated stamper, and a process for transcribing the shape of grooves from a stamper by injection molding.
However, the above described printing method has the disadvantage in that there is a limit to storage capacity because a pattern having a constant line width or less can not be printed. In addition, the other methods for forming groove-shaped guide tracks have the disadvantage in that it takes a lot of time to manufacture an optical memory device because continuous processing can not be performed, causing difficulty in reducing cost.
Furthermore, a sheet-like substrate material is generally wound like the roll, so that a substrate is slightly warped. Such warping of the substrate is not preferable in optical characteristics and causes difficulty in the manufacturing of an optical memory device with high precision. Therefore, under the present circumstances and in accordance with the invention, warping is eliminated by heat treatment.